Earlier Microsoft has announced that its Windows 8 has reached RTM stage and will be available to TechNet and MSDN users from 15 August onward and GA will be on 26 October.
Now Microsoft has also announced that Windows RT has also reached RTM stage. Windows RT is build for ARM based chip running tablets like Surface. Windows RT comes pre-installed with MS Office 15 in it.
Many companies like NVIDIA, Qualcomm and Texas Instruments are building ARM based tablets which will run Windows RT. Microsoft has already announced that they will not sell Windows RT standalone, it will only be shipped with pre-installed in tablets.
You wont be able to run Windows RT on your desktop and that’s why it will only support Metro apps not any Desktop apps. General Announcement of Windows RT will be on same day as of Windows 8, i.e, 26 October.